1. Field of the Invention
The present invention relates to an electrochemical cell such as a non-aqueous electrolyte cell and an electric double layer capacitor utilizing electric double layer theory, and to a fabrication method of the same.
2. Description of the Related Art
The electrochemical cell such as the non-aqueous electrolyte cell and the electric double layer capacitor is used for a backup power source of clock functions, a backup power source of semiconductor memories, an auxiliary power source of electronic devices such as a microcomputer and an IC memory, a battery of solar-powered clocks, and a power source for driving motors. With the realization of non-volatile semiconductor memories and reduced power consumption of clock function devices, the electrochemical cell is not required for large capacity and large current so much. Instead, for the needs of the electrochemical cell, an increasing demand is that components are placed on a mounting board applied with solder cream and are mounted in a reflow furnace controlled at a solder melting point (200 to 260° C.), as similar to ICs, and quartz and SAW devices. Furthermore, it is required for high-density mounting and the reduction in size and thickness as well as the ICs, and quartz and SAW devices
Traditionally, the electrochemical cell such as the non-aqueous electrolyte cell and the electric double layer capacitor is packaged in a metal case shaped in a coin or button (for example, see Patent Reference 1).
FIG. 12 depicts a cross-sectional view for describing a traditional electrochemical cell. It is configured of a positive electrode case 61 of stainless steel having the upper end surface side opened in a circular shape for housing a positive electrode active material 601 and a negative electrode active material 603 as electrodes and a separator 602, and of a circular negative electrode case 63 fit into the positive electrode case 61 through a circular gasket 62 of insulating resin. Moreover, when surface mounting is required, the cell has a positive electrode terminal 65a welded with the positive electrode case 61 and a negative electrode terminal 65b welded with the negative electrode case 63.
Patent Reference 1 JP-A-2002-190427
For the electrochemical cell such as the traditional non-aqueous electrolyte cell and the electric double layer capacitor described above, a sealing structure is conducted for securing heat resistant properties in solder reflow in which the gasket 62 in an annular shape is pressed by the positive electrode case 61 circularly opened and the circular negative electrode case 63 for crimping. For securing the heat resistant properties and sealing properties of the electrochemical cell, the cell is shaped in a coin or button. However, since the packages of ICs, and quartz and SAW devices placed on the mounting substrate are formed in a rectangular shape, space is created when the electrochemical cell is arranged. When this space is used effectively, a little over 20 percent increase is expected in the storage capacity of the electrochemical cell. Furthermore, the positive electrode case 61 is formed of a metallic material, but it is short-circuited when the positive electrode case 61 is contacted with the negative electrode terminal 65b. Therefore, space needs to be secured. More specifically, as shown in FIG. 12, the negative electrode terminal 65b needs to extend outside over the outer diameter of the positive electrode case 61, causing the space occupied on the mounting substrate to be further increased. Thus, dead space is created to increase the occupied area when the cell is arranged on the mounting substrate, and it is difficult to increase the capacity per unit area on the mounting substrate. Moreover, when the positive electrode terminal 65a and the negative electrode terminal 65b are mounted on the positive electrode case 61 and the negative electrode case 63, the individual components are overlaid and welded with each other as shown in FIG. 12. Therefore, the total thickness of the electrochemical cell is increased to hinder the reduction in thickness while the number of process steps of mounting the positive and negative electrode terminals is increased, causing high price.